Transmitting system



TRANSMITTING SYSTEM Filed Dev. 22, 1928 f\ 6 a '75" 7) f\ \QQQQ.) I

I I I I INVENTOR. (BM Q0, gg

BY 3 W ATDTORNEY Patented June 14, 1932 FATE CLINTON VJ. HOUGH, FBOONVILLE, NEW YORK, ASSIGNOR, BY MESNE ASSIGNMENTS, TO \VIRED RADIO, IN0., OF NEW YORK, N. Y., A CORPORATION OF DELAWARE TRANSMITTING SYSTEMApplication filed December 22, 1928. Serial No. 328,009.

My invention relates to transmitting systems in general and morespecifically to continuous wave transmitters.

An object of my invention is to provide a transmitting system whereinthe generated carrier energy is modulated with a plurality of signals.

Still another object of my invention is to provide a transmitting systememploying a single carrier frequency by means of which a plurality ofdifferent sources of audio frequencies are transmitted.

These objects are accomplished by the provision of two 3-element vacuumtubes connected in a series opposing relationship with the modulatingfrequency source so that only one tube is operative at any one time, theother being biased so negatively on each alternative half cycle of themodulating frequency that it ceases to transmit for that period.

The objects of this invention are somewhat similar to those of mycopending applica tion Serial No. 338,146, filed February 7, 1929, fortransmitting and receiving systems. In that application, however, asystem is shown in which two distinct signals may be transmitted on onecarrier wave, the means employed being adapted to establish a potentialnodal point in the circuit thereof so that signal modulations may beindependently impressed at antinodal points on either side of the node.In this manner the high frequency energy is locally absorbed on one sideof the nodal point while being transmitted from that portion of thecircuit on the other side of the nodal point.

A better understanding of my invention can be had from the specificationfollowing and from the accompanying drawing wherein: The figure is aschematic circuit diagram showing the transmitting system of myinvention.

In high frequency continuous wave transmitting systems, thermionic tubesare usually employed in suitable oscillatory circuit arrangements forgenerating the high frequency electrical energy. This high frequencyenergy is modulated in accordance with a lower frequency, usually audiofrequency, which lower frequency is received at the receiving station.The high frequency energy is generally referred to as the carrierfrequency and it is common to refer to the lower frequency as modulatingfrequency which is superimposed upon the higher frequency. Therelatively narrow allotment of frequency bands available forcommunication by space radio gives rise to the desirability of eitherincreasing the frequency band or improvements in the apparatus wherebythe frequency band occupied by a given transmitting station will bereduced. Other needs created by the demand for selective or secretcommunication must be satisfied without employing wide bands offrequency and thereby depriving others from the use of these bands. Manysystems of multiplexing have been introduced which systems generallyhave some disadvantages which make the same impractical for adoption.The transmitting system of my invention provides a simple, efficient andinexpensive arrangement whereby a plurality of individual messages orprograms may be transmitted by employing a single carrier frequency. A.better understanding of the system I employ can be had by referring tothe specification following and to the accompanying drawing.

The figure of the accompanying drawing is a schematic pircuit diagram ofthe transmitting system of my invention. A source of high frequencyelectrical energy 1 having a frequency value of 1% is associated with afrequency multiplier 2 adapted to multiply the frequency of the energyfrom source 1 to a frequency of 2a. Inductance coils 7 and 8 areconnected in series and the series connected with source 1. Inductances7 and 8 are associated with inductances 7a and 8a respectively and areadapted to transfer high frequency energy thereto. Inductances 7a and 8aare connected in series with inductances 5 and 6 respectively. Theseries connections of inductances 6 and 8a comprise the input circuit ofthermionic tube 10. The series connections of inductances 5 and 7acomprise the input circuit of thermionic tube 9. Thermionic tubes 9 and8 are illustrated as of the triode type having cathodes, controlelectrodes and anodes. It is obvious that thermionic tubes of anysuitable design may be employed. Modulating circuit including microphone.3 and inductance 5a is associated with inductance 5. A modulatingcircuit including microphone 4 and inductance. 6a is associated withinductance 6. The output circuits of thermionic tubes 9 and 10 includeinductances 11 and 12 respectively. Inductances 11 and 12 are associatedwith inductances 14 and 15 respectively, the latter two inductancesconnected in series with i1iductance 13 and associated with the outputof frequency multiplier 2. A load circuit 13a is associated withinductance 13 and may comprise a space. radio radiating system asillustrated, a wired radio system or subsequent amplifier circuits.

The high frequency electrical energy from source 1 is alternating inpolarity causing the control electrode of thermionic tube 9 to besupplied with a positive polarity in respect to the polarity ofthecontrol electrode of thermionic tube 10. The next instant the controlelectrode of thermionic tube 9 is supplied with a potential of negativepolarity in respect to the polarity of the potential supplied thecontrol electrode of thermionic tube 10. In this manner the controlelectrodes of thermionic tubes 9 and 10 are alternately and oppositelybiased by having their circuits coupled to the high frequency electricalenergy circuit so that each tube is rendered inoperative. when its gridbecomes negatively biased. Thermionic tubes 9 and 10 therefore operatein alternate order. Since individual modulating circuits 3-500 and 1-6aare associated with thermionic tubes 9 and 10 respectively, it followsthat the resistance of these tubes is varied first by one microphone andthen by the other. It is obvious that microphones 3 and i may bereplaced by any source of low frequency energy. Inductances 11 and 12,associated with inductances 14 and 15 respectively, absorb certainenergy from the output circuit of frequency multiplier 2 and hencereducethe amount of energy in load circuit 13a. Since the carrier frequency istwice that of the modulating frequency in inductances 11 and 12,alternate cycles of the carrier energy are modulated alternately bymicrophones 3 and 4;.

Many modifications of my invention are possible. The accompanylngdrawing is only representative and it is not intended to limit myinvention thereby. The several inductive and electromagnetic relationsof the several circuits may be replaced by resistor, impedance andcapacity arrangements and other forms of coupling well known to thoseskilled in the art. It is to be understood that the embodiments of myinvention shall not be restricted by the foregoing specification or bythe accompanying drawing but only by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. A transmitting system comprising in combination, a source of highfrequency electrical energy, a plurality of thermionic tubes, means forincreasing the internal resistance of said tubes to inoperativeness inalternate. order, means for multiplying the frequency of said highfrequency energy, the output circuits of said thermionic tubes beingassociated with said energy of multiplied frequency value and individualmodulating circuit arrangements associated with said thermionic tubes.

2. A transmitting system comprising in combination a source of highfrequency electrical energy, means for multiplying said frequency, aplurality of thermionic tubes having associated input circuits, outputcircuits and individual modulating circuits, said input circuits beingblocked by said source of high frequency energy alternately by biasingsaid tubes beyond their operative points said output circuits receivingsaid modulated frequencies in accordance with the period of operation ofsaid tubes.

3. The method of transmitting two distinct signals on one carrier wavewhich comprises modulating the positive portion of a high frequency waveby one of said signals, modulating the negative portion of said highfrequency wave by the other of said signals, multiplying said highfrequency wave to obtain a carrier wave and superposing the modulationsobtained in the aforesaid manner upon said carrier wave.

4:. A transmittingsystem comprising a generator of radio frequencyenergy, a frequency multiplier coupled to said generator, a modulatingcircuit including a thermionic tube the grid of which is alternatelynegatively blocked by coupling with radio frequency impulses of onepolarity and then made responsive to monulations of audio frequency, asecond modulating circuit including a thermionic tube the grid of whichis alternately negatively blocked by coupling with radio frequencyimpulses of the opposite polarity to that which blocks the grid of thefirst said tube and then made responsive to modulations of audiofrequency, said modulations to which said tubes are made responsivebeing of different origin, and means to superpose said modulations uponthe output of said frequency multiplier.

In testimony whereof I afliX my signature.

CLINTON W. HOUGH.

